This study investigates weathering-related volume change by examining strong weathering of dense andesite. Andesite lava erupted on land during the Early Cretaceous, with the weathered rock consisting of a red-to-yellow-tinged matrix. The strongly weathered zone extends from 30 m to 40 m below the surface. Plagioclase disappears from the strongly weathered zone where kaolinite and halloysite form. In addition, the crack zone is several meters in width and lies between the strongly weathered zone and the fresh andesite zone.
Corestones consisting of fresh andesite have a diameter of about 20 cm and are often overlain in the upper part of the crack zone. In addition, rindlet-covered corestone 3 mm to 3 cm wide is observed around the fresh andesite zone. Na and Ca completely disappear from rindlet. Inversely, Ti and Zr are clearly concentrated in rindlet. These elements became mobile through weathering.
The clinopyroxene distribution uses the frequency ratio of high Fe-content pixels, indicating the same profiles for corestone and rindlet. The rock mass volume does not change through this weathering.
Ti increasing in rindlet is derived from the titanomagnetite dissolution. Plagioclase produces kaolinite and halloysite, and porosity increases with kaolinite and halloysite crystallization.
The results show that isovolumetric reaction occurring despite dissolution and crystallization with strong weathering. We consider that this weathering leads to surface slope changes.
